The present invention provides time dependent indicators including but not limited to timers and time/temperature indicators that preferably have a high level of accuracy and are easy to read. The invention also provides indicators that have uses as greeting cards, calendars, announcements, game pieces, novelty items, etc.
Applications for time indicators may be divided into two broad categories. The first category requires time indicators that measure not only time but take into account the actual cumulative thermal exposure of the product. This objective is accomplished by having the rate of change of the indicator increase with temperature according to a desired function. Some such indicators exhibit a threshold temperature, below which the indicator does not change. Others respond more continuously to changes in temperature. This type of time indicator is typically referred to as a xe2x80x9ctime-temperature indicatorxe2x80x9d.
The second category of applications requires time indicators in which the thermal sensitivity is minimized. Thus, in this application the time indicators work much like a timepiece, giving a visual indication of time elapsed. This type of time indicator is frequently referred to as a xe2x80x9ctimerxe2x80x9d.
Timers and time-temperature indicators are known which operate by chemical reaction mechanisms, diffusion mechanisms, and capillary driven fluid wicking mechanisms. For a discussion of several types of indicators, reference is made to Dee Lynn Johnson, Indicating Devices, in The Wiley Encyclopedia of Packaging Technology, 400-406 (John Wiley and Sons, 1986).
A selectively activated time-temperature integrating device providing a visually observable indication of cumulative thermal exposure is disclosed in U.S. Pat. No. 5,667,303 (Arens, et al.). In this device a viscoelastic material migrates into a porous matrix at a rate varying with temperature and progressively changes the transmissivity of light through the porous film to provide a visually observable indication. The viscoelastic material can comprise a pressure sensititve adhesive. The visually observable indication comprises latent indicia which are not initially visible later and become visible. The device is activated by lamination of a front and back part.
A time-temperature indicator that operates on diffusion properties and provides a visual indication by means of a chemical reaction is disclosed in U.S. Pat. No. 5,053,339 (Patel). This patent discloses a color changing device for monitoring the time-temperature history of perishable products containing an activator tape and an indicating tape. The activator tape contains an activator composition matrix that includes an activating composition such as an organic acid. The indicating tape includes an indicating composition matrix that includes an indicating composition such as an acid-base dye indicator. One or both of the matrices is a pressure sensitive adhesive. The indicator produces a color change as the activating composition diffuses out of the activator matrix and into the indicator matrix and chemically reacts with the indicating composition in the indicating matrix. The color intensifies with time and temperature as more activator composition diffuses into the indicator matrix and reacts.
Another type of indicator is disclosed in U.S. Pat. No. 3,954,011 (Manske). This patent discloses an indicator including a porous fluid carrying pad, a saturant material, a wick material for the saturant, and an indicator means whereby the progress of the saturant from the porous carrying pad along the wick material can be visibly indicated and used to measure the passage of time, the exposure to a given minimum temperature, or a time-temperature relationship. When the saturant is chosen so as to be in a liquid state at the intended storage temperature, the indicator indicates the passage of a time interval as the liquid progresses along the wick. The saturant may instead be selected so as to be solid at desired storage temperatures at which frozen foods are stored and to become liquid at temperatures at which the food is thawed. The saturant will remain solid while the indicator is at the desired storage temperature. The saturant will melt to a penetrating state and then progress along the wick while the indicator is above the predetermined temperature, thereby indicating the passage of time above the predetermined temperature. A plurality of saturant materials having varying freezing points, each having its own wicking path, can be used to indicate time of exposure to discrete predetermined temperature ranges.
Another indicator is disclosed in U.S. Pat. No. 4,428,321 (Arens). This patent discloses a device which provides a visual indication that permissible time within a predetermined temperature range has been exceeded. The device includes an opaque microporous sheet with a colored stratum on its back and a transparent fusible coating bonded to its face. The fusible coating is a solid solution of an amorphous rubbery polymer dissolved in a crystallizable solvent such as wax. The solvent has a melting point below the lower end of the predetermined temperature range and the polymer has a glass transition temperature below the lower end of the predetermined temperature range. Below the melting temperature of the solvent, the composition is a non-penetrating solid. When the indicator is heated to a predetermined temperature, the solid wax solvent melts and dissolves the rubbery polymer, resulting in a liquid penetrating state which gradually penetrates the microporous layer. The refractive index of the polymer and wax composition is essentially the same as that of the solid component of the microporous layer, rendering the microporous layer gradually transparent.
U.S. Pat. No. 4,154,107 (Giezen et al.) describes a time temperature indicating device having an indicator layer and a signaling component in a reservoir which migrates to the indicating layer and causes the indicator layer to undergo a visually perceptible change.
U.S. Pat. No. 2,896,568 (Pryor et al.) discloses a temperature indicating device comprising substances introduced in liquid form into a plurality of wells and frozen in situ, which substances melt and migrate out of the wells as a result of gravity or capillary attraction or both and the migration may be detected by observation.
U.S. Pat. No. 3,999,946 (Patel et al.) describes a time-temperature history indicator, which contains compositions containing at least two conjugated acetylene groups which exhibit sequences of irreversible color changes at combinations of time and temperature. The device may be supported on the surface of a product or on a substrate.
Other types of known time indicators, which are generally short-term time indicators, are based on the gradual diffusion or migration of a substance such as an ink from one substrate through another substrate, i.e. in a path perpendicular to the surface of the substrate. After the ink or other substance migrates through the substrate(s) it is viewed on a display surface to thereby indicate that the predetermined time period has elapsed.
U.S. Pat. No. 4,903,254 (Haas) describes a time indicator comprising a number of layers that are adhered together. The indicator has a front part and a rear part. The rear part comprises an ink pattern layer upon rear support member and the front part comprises a transparent support member and an opaque adhesive layer. The adhesive layer is capable of dissolving the ink pattern and has a front ink display surface. Contacting the front part and rear part activates the dissolution and migration of ink from the ink pattern layer to the front ink display surface.
U.S. Pat. No. 5,364,132 (Haas et al) describes a reusable self-expiring security identification badge including a base substrate having a void indicia area, an ink substrate having an expired indicia area of a soluble ink and an adhesive surface and an overlay substrate having an ink dissolver and a display surface. When the badge is issued, the inked substrate is attached to the base substrate, the inked substrate covering the void indicia area. The overlay substrate is then placed over and attached to the inked substrate, the ink dissolver in contact with the ink substrate. The ink dissolver of the overlay substrate contacts and co-acts with the soluble ink of the inked substrate to dissolve the ink and allow the ink to migrate through to the overlay substrate to the display surface, where it can be visually perceived, in a preselected time interval.
U.S. Pat. No. 3,520,124 (Myers) describes timer device based on two or more reactive materials which react either physically or chemically over a predetermined period to produce a termination signal. The reacting materials are carried on a base member and separated by a barrier preventing contact. Elimination of the barrier commences the timer reaction.
U.S. Pat. No. 4,212,153 (Kydonieus et al.) describes a laminated indicator that changes in a visually perceptible mode with the passage of time. The indicator comprises at least two layers, whereby the molecular migration of an agent in an interior layer to the outermost surface of the exterior layer causes a change which is visually perceptible.
U.S. Pat. No. 5,045,283 (Patel) describes a device comprising an activator tape, which includes an activator composition in an activator matrix, and an indicating tape that includes an indicator composition in an indicator matrix. The tapes are adhesively bound together to form a wedge-shaped composite matrix. The activating composition diffuses through the increasingly thicker composite matrix to contact the indicating composition to produce a visually observable color change at the temperature being monitored. The color change appears as a moving boundary at the color/non-color interface that moves transversely along the length of the device toward the thicker end.
U.S. Pat. No. 5,107,470 (Pedicano et al.) describes a time color indicator comprising first segment comprising a transparent non-permeable web coated on the bottom side with an opaque non-curing coating and a release sheet removably attached to the coating. The top side contains a message printed with an ink containing a migrating agent. The second segment comprises a transparent non-permeable web coated on the bottom side with an opaque non-curing coating. A portion of the bottom side of the second segment is adhered to the first segment top surface, the remainder is covered with a release paper. When the release paper is removed the second segment overlies and adheres to the printed portion of the first segment obscuring the printed area until the printed message migrates through the opaque layer to display the message.
U.S. Pat. No. 5,446,705 (Haas et al.) describes a time indicator that changes color or produces an image or information after a specific time interval. The time indicator includes a base with color dye deposited on a first surface; and a substrate having an adhesive on a first surface thereof, the adhesive positioned at discrete locations on the first surface of the substrate. When the substrate and the base are put into adhesive contact with each other, the adhesive contacts and co-acts with the colored dye to dissolve the dye and permit the dye to migrate through the adhesive to cause a color change visible through the substrate. The discrete adhesive inhibits lateral migration of the dye to preserve the image or information of the dye in a clear and/or understandable condition.
U.S. Pat. No. 4,643,122 (Seybold) describes a diffusion controlled security tag comprising a carrier containing a solution of a compound which changes color upon diffusion or evaporation of the solvent. Preferably, the carrier is enveloped in a barrier film which controls the rate of diffusion/evaporation of the solvent from the carrier, such that a change in color of the carrier indicates undesirable storage or product tampering.
U.S. Pat. No. 5,058,088 (Haas) describes a time indicator which includes a first substrate having first and second surfaces and at least two indicia areas on the first surface. A second substrate having first and second surfaces is also provided. A first chemical agent is provided on each of the indicia areas and a second chemical agent is provided on the first surface of the second substrate. The first surfaces of each substrate overlay and are in contact with each other, the chemical agents coacting to cause a visually perceptible change at one of the second surfaces overlaying the first indicia area in a first selected time interval and a visually perceptible change in said second surface overlaying the second indicia area in a second selected time interval, the first selected time interval differing from the second selected time interval.
Other known timers and time-temperature indicators are based on the migration of liquids or jelly through wicks to indicate the passage of time or thermal exposure.
U.S. Pat. No. 4,229,813 (Lilly et al) describes a time indicator which includes a reservoir of silicone oil contained in a frangible housing which upon crushing releases the silicone oil which is slowly absorbed onto and moves up a porous strip at a rate which is a function of time. One side of the strip is printed with an oil soluble ink, while the other side is unprinted. The printed side of the strip is laminated to an unprinted strip. As the silicone oil moves up the strip, the oil contacts the ink causing a dye in the ink to migrate from the printed side to the unprinted side, thus providing a measurable color front moving up the strip.
U.S. Pat. No. 4,382,700 (Youngren) describes an indicator which contains a capsule of mineral jelly which is in contact with a wick, such that the mineral jelly diffuses into the wick in accordance with the changes in ambient temperature over a period of time. The amount of diffusion is indicated by an apparent change in color of the wick.
U.S. Pat. No. 4,408,557 (Bradley et al.) describes a time indicator wherein a migrating carrier mixture is contained in a confined area above a base layer. An absorptive layer is disposed on the base layer and accepts the carrier mixture at a predetermined rate upon removal of a barrier to activate the timer.
U.S. Pat. No. 4,292,916 (Bradley et al.) describes a time indicator in which components or a carrier mixture react physically and chemically with one or more receptive layers causing prominent changes.
U.S. Pat. No. 4,432,656 (Allmendinger) describes a time/temperature integrator for indicating the history of a deep frozen product through diffusion of water along a cellulose wick.
U.S. Pat. No. 4,629,330 (Nichols) describes a color change indicator of time and temperature. The device includes a reservoir of liquid having a predetermined index of refraction and a rate of evaporation. The liquid is covered by an opacifying layer of microporous material. The opacifying layer has an index of refraction approximately the same as that of a liquid and has an open cell network of pores for absorbing liquid from the reservoir. The layer is in a first radiation scattering condition when the liquid occupies the opacifying layer and after a specified period of time in a second scattering condition when the liquid is depleted from the opacifying layer.
U.S. Pat. No. 3,243,303 (Johnson) discloses a temperature monitor including an absorbent body having an indicating area on a surface thereof, and a fluid composition for producing a visual indication at the indicating area. The fluid composition preferably is arranged for absorption by the absorbent body at a zone remote from the indicating area, and the fluid composition travels to the indicating area under certain temperature conditions and provides a visual indication thereat.
U.S. Pat. No. 4,195,058 (Patel) describes a device for monitoring time-temperature histories in which a vapor is allowed to permeate through a permeable vapor barrier to contact a liquid polydiacetylene indicator to provide a color response after a predetermined period of time.
Other time or time-temperature indicators rely primarily upon chemical reactions to cause a visually perceptible change over a desired time period rather than the migration of fluids or compounds. These indicators rely upon exposure to light and/or oxygen to trigger the chemical reaction. Examples of these types of indicators include U.S. Pat. No. 2,337,534 (Barber), U.S. Pat. No. 3,018,611 (Biritz), U.S. Pat. No. 3,480,402 (Jackson), U.S. Pat. No. 4,432,630 (Haas), U.S. Pat. No. 4,542,982 (Haas), U.S. Pat. No. 4,779,120 (Haas) U.S. Pat. No. 4,812,053 (Bhattacharjee et al.), U.S. Pat. No. 4,917,503 (Bhattacharjee et al.), and U.S. Pat. No. 4,987,849 (Sherman).
It is desirable to have indicators that can provide a visual indication of a predetermined period of time. This type of indicator would be useful in a variety of applications, such as, for example, monitoring the useful life of a perishable item. Such perishable products include, but are not limited to, foods, food additives such as aspartame, biological materials, drugs, cosmetics, photographic supplies, and vaccines. Time indicators would also be useful to monitor time elapsed and expiration in a variety of applications that do not involve perishable items. For example, security badges could have a time indicator to mark expiration. Time indicators could also be used as reminders that a certain task and/or items need to be completed, replaced or renewed. Time indicators could also be used in novelty items and gaming pieces.
One simple way of providing an indication of when the useful life of a perishable product has expired is to mark each product with a suggested date by which that product should be used. However, there is a shortcoming in this method in that the actual useful life of perishable products is dependent on the temperature history to which the product is exposed because the rate of degradation of a perishable product usually increases with increasing temperature. In other words, a perishable product will generally have a shorter remaining useful life when exposed to a certain period at a relatively high temperature than when exposed to the same period at a relatively low temperature. More broadly, the rate of change of a particular property or characteristic of any material or product may increase with increasing temperature. Therefore, marking a product with a xe2x80x9cuse byxe2x80x9d date must be based on assumptions about the anticipated thermal exposure of the particular product. However, the actual exposure cannot always be predicted or controlled, hence the need for a time-temperature indicator.
Of particular concern is that the rate of degradation or other change at a given temperature is different from product to product, as is the variation in the rate of degradation with temperature. Some products show a greater increase in rate of change for a given temperature increase than other products. One useful way to quantify this is with reference to the Q10 of a reaction. The Q10 is an indication of how much faster a reaction (such as chemical change, microbial growth, or enzymatic spoilage of a perishable product) occurs in response to a 10xc2x0 C. increase in temperature wherein T is provided in xc2x0 C.:
Q10=(Rate of change at T+10xc2x0 C.)/(Rate of change at T)
For example, most perishable foods stored under refrigeration have Q10 values based on spoilage by microbial growth, which have Q10 ranges from about 2 to 10. In other words, the rate of degradation will increase by a factor of from about 2 to 10, depending on the particular food, in response to an increase in temperature of 10xc2x0 C. Other perishable items such as drugs, biological materials, and vaccines will likewise show different Q10 values for each particular item.
The Arrhenius relationship is also a useful tool for quantifying the effect of temperature on many chemical and physical processes. The Arrhenius relationship is:
xe2x80x83k=ko exp(xe2x88x92Ea/RT)
where
k=the rate constant as a function of temperature T (Kelvin);
ko=the preexponential factor;
R=the ideal gas constant (1.99 Kcal/mole K); and
Ea=the activation energy in Kcal/mole.
It is possible to perform experiments with particular perishable items to determine rates of degradation at various temperatures, and then apply the Arrhenius relationship to these experiments to calculate a measured activation energy (Ea) for each particular perishable item within a given temperature range. It has been observed that for many perishable items, such data will closely fit the Arrhenius equation, which assumes that Ea is independent of temperature. As with the Q10 value, the particular value of Ea will vary with the particular item to be monitored. For a further discussion on the analysis and quantification of the degradation of foods, reference is made to Theodore P. Labuza, Shelf-Life Dating of Foods, pp. 41-87 (Food and Nutrition Press, Inc. 1982), incorporated by reference herein.
Therefore, it is seen that there is a need to provide an indicator of cumulative thermal exposure in which the Q10 or Ea of the rate of providing a visual indication of cumulative thermal exposure can be approximately matched to the Q10 or Ea of the change of the object to be monitored. The indication of cumulative thermal exposure can thereby be approximately matched to the cumulative degradation of the object to be monitored.
This is not the case for time indicators that are meant to be used as timers. Timers should have a minimal dependence on temperature. A perfect timer would have a Q10 value of 1 or alternatively an Ea value of 0. However, virtually any timer will be slightly dependent on temperature.
For both time-temperature indicators and timers it is also desirable to provide an indicator that has an inactivated state in which it may be stored at varying temperatures for long periods of time without changing. While in some cases it may be acceptable to activate the indicator while it is being fabricated, it is preferable that the indicator be capable of selectively being switched to an activated state before, after, or at the time it is affixed to an object to be monitored, after a container is filled with contents to be monitored, after opening a container of contents to be monitored, or at any other desired time after the indicator is fabricated. Such an indicator, whether activated or inactivated, should not be deleteriously affected by environmental factors such as humidity and light.
A problem that generally exists in both time-temperature indicators and timers that rely upon a color change to indicate the passage of time, is that they gradually change color over a long period of time and it is difficult to ascertain the actual completion of the time interval. Earlier time indicator technologies are generally based on color changes that occur by a diffusion process that begins upon activation. In these systems, it is difficult for the observer to identify and determine exactly when the image or color indicates that the predetermined time interval has elapsed. This is because in time indicators based on diffusion, the time interval for the image or color appearance is proportional to the predetermined time for which the time indicator has been designed. Thus, for example, in a three month indicator, the time indicator stays in its xe2x80x9coffxe2x80x9d state for about a month, after which, the entire indicator starts to change color. After about three months, the observer sees a definite color change of, say 10-20% tint. During the time interval between one and three months, the time indicator is in a xe2x80x9cgrey areaxe2x80x9d, i.e., xe2x80x9cThe Grey Timexe2x80x9d, between expired and unexpired and is subject to interpretation by the viewer. This lack of a sharp transition time is the problem with known time indicators based on diffusion.
Other indicators that utilize fluid migration along a wick while not subject to the Grey Time problem have other drawbacks. These indicators, because of the nature of the wicking materials, suffer from the drawback of accuracy and repeatability in the measurement of time or time and temperature. The wicking materials unlike the microstructed substrates of the invention do not have a predetermined structure. Since the pore structure in wicking material is not easily controlled, the behavior of the indicator is often insufficient for timing or time/temperature indicator needs.
The articles of the invention are preferably capable of solving the problems with the known indicator devices.
The present invention provides time dependent indicators including but not limited to timers and time/temperature indicators that preferably have a high level of accuracy and are easy to read.
The articles of the invention are preferably self-contained and preferably allow for activation on demand. By appropriate selection of the fluid (temperature sensitive or relatively temperature insensitive, for example) the article may function, for example, as a time/temperature indicator or a timer. The article is preferably capable of providing a highly accurate readout on progress and end-point determination.
The articles of this invention can optionally be made to comprise innocuous and nonreactive materials,thus providing a safer article over those which do not employ such materials. Preferably the article of the invention can remain in an inactivated state for a long period of time without suffering deleterious affects.
One aspect of the present invention provides an article comprising:
(a) at least one substrate, each substrate(s) having a microstructured surface, wherein the microstructured surface of each substrate defines a plurality of channels;
(b) at least one fluid, wherein the fluid(s) are separated from the substrate(s) until activation of the article is desired;
wherein the article is designed such that it can be manipulated at a desired point in time to allow contact of the fluid(s) with at least some of the channels of at least one of the substrate(s) in order to activate the article; and
wherein the article is designed in such a manner as to provide an indication of the progress of the fluid(s) as it migrates through the channels of the substrate(s).
An article of the invention may comprise only one fluid and only one substrate, for example. In some embodiments the article of the invention may comprise a plurality of the fluids. In some embodiments of the invention the article may comprise a plurality of the substrates. In some embodiments of the article of the invention the article may comprise a plurality of the fluids and a plurality of the substrates.
Preferably the channels of each of the substrate(s) are interconnected. Preferably each fluid is selected from the group consisting of viscous fluids, viscoelastic fluids, and combinations thereof.
In some embodiments of the article of the invention each substrate may be retroreflective such as a cube-corner retroreflective sheeting.
In one embodiment of an article of the invention each substrate is retroreflective and wherein the progress of each fluid as it migrates through the channels is evidenced by frustration of the total internal reflectance in the retroreflective substrate.
In a preferred article of the invention the article is designed such that there is essentially no leakage of fluid(s) from the article prior to or subsequent to activation.
In the article of the invention each fluid has a fluid flow front as it migrates through the channels and each fluid front variation is preferably less than about 5 mm, more preferably less than about 3 mm, and most preerably less than about 1 mm.
The article of the invention may, for example, be selected from the group consisting of timers, time/temperature indicators, game pieces, greeting cards, announcements, invitations, calendars, etc.
When the article is a timer it may according to the Capillary Action Test Method display a time when in a vertical position within about xc2x150 percent, more preferably about xc2x125 percent, and most preferably about 10 of an identical timer in a horizontal position.
In some embodiments wherein the article is a timer, the article may display a time at an expiration point which is within about xc2x125 percent of the actual elapsed time, more preferably within about xc2x110 percent of the actual elapsed time, and most preferably within about xc2x15 percent of the actual elapsed time.
In one embodiment of the article of the invention each substrate has two opposing major surfaces, one being identified as the first major surface and the other being identified as the second major surface, wherein the second major surface has a series of essentially parallel channels therein, wherein the channels are essentially of uniform length and uniform shape.
In another embodiment of the article of the invention each fluid is separated from the substrate(s) by a barrier(s) until activation of the article is desired, wherein the barrier can subsequently be manipulated at a desired point in time to allow contact of the fluid(s) with at least some of the channels of at least one of the substrates.
In another embodiment of the article of the invention the article further comprises a covering which sufficiently encases the substrate(s), the barrier(s), and the fluid(s) in such a manner as to allow the fluid(s), upon activation of the article to travel along the channels of the substrate(s) but not to substantially escape from the article, wherein at least a portion of the covering is sufficiently transparent and wherein the coloring and levels of transparency of the covering, substrate(s) and fluid(s) are selected to allow an observer to the view the fluid(s) with the unaided eye as the fluid(s) travel along the substrate channels.
In another embodiment the article of the invention comprises:
(a) a plurality of substrates, each substrate having a microstructed surface, wherein the microstructured surface of each substrate defines a plurality of channels;
(b) a fluid, wherein the fluid is separated from the substrates until activation of the article is desired;
wherein the article is designed such that it can be manipulated at a desired point in time to allow contact of the fluid with at least some of the channels of each substrate, either simultaneously or in any desired order, in order to activate the article; and
wherein the article is designed in such a manner as to provide an indication of the progress of the fluid as it migrates through the channels of each substrate, wherein the article is designed to prevent fluid from migrating from one substrate onto another substrate.
An article of the invention may be designed such that the fluid contacts at least some of the channels of each substrate simultaneously upon activation of the article. In an alternative embodiment an article of the invention may be designed such that the fluid contacts at least some of the channels of each substrate consecutively upon activation of the article.
In another embodiment of the invention the article may comprise a plurality of substrates which are positioned adjacent to each other. In another embodiment of the article of the invention the article may comprise a plurality of substrates which are stacked one upon another. In another embodiment of the invention the article may comprise a plurality of substrates wherein the plurality of substrates are all retroreflective. In another embodiment of the invention the article may comprise a plurality of substrates In another embodiment of the invention the article may comprise a plurality of substrates wherein the plurality of substrates are all non-retroreflective. In another embodiment of the invention the article may comprise a plurality of substrates wherein each of the substrates has a different fluid flow rate with respect to the fluid. In another aspect the article of the invention comprises:
(a) a plurality of substrates, each substrate having a microstructured surface, wherein the microstructured surface of each substrate defines a plurality of channels;
(b) a plurality of fluids, wherein each fluid is separated from the substrates until activation of the article is desired;
wherein the article is designed such that it can be manipulated at a desired point in time to allow contact of each the fluids with at least some of the channels of at least one of the substrates, either simultaneously or in any order desired to activate the article;
wherein the article is designed in such a manner as to provide an indication of the progress of each fluid as the fluid migrates through the channels of ones of the substrates; wherein the article is designed to prevent fluid from flowing from one substrate onto another substrate.
In one embodiment of the article of the invention the number of fluids is equal to the number of substrates. In another embodiment of the article of the invention the article is designed such that each fluid contacts at least some of the channels of a separate substrate simultaneously upon activation of the article. In another embodiment of the article of the invention the article is designed such that each fluid contacts at least some of the channels of a separate substrate consecutively upon activation of the article. In another embodiment of the article of the invention the article comprises a plurality of substrates wherein the plurality of substrates are positioned adjacent to each other. In another embodiment of the article of the invention the article comprises a plurality of substrates the plurality of substrates are stacked one upon another.
In another embodiment of the article of the invention the article comprises a plurality of substrates wherein the plurality of substrates are all retroreflective. In another embodiment of the article of the invention the article comprises a plurality of substrates wherein the plurality of substrates are all non-retroreflective. In another aspect the article of the invention comprises:
(a) at least one substrate having two opposing major surfaces, one being identified as the first major surface and the other being identified as the second major surface, wherein the second major surface is a microstructured surface which defines a plurality of channels, the channels having inlets;
(b) at least one fluid, wherein the fluid(s) are separated from the substrate(s) by a barrier(s) until activation of the article is desired, wherein the barrier(s) can subsequently be manipulated at a desired point in time to allow contact of at least one of the fluid(s) with an end of the second major surface of at least one of the substrate(s) at inlets to at least some of the channels;
(c) a covering which sufficiently encases the substrate(s), the barrier(s), and the fluid(s) in such a manner as to allow the fluid(s), upon activation of the article to travel along the channels of at least one of the substrate(s) but not to substantially escape from the article, wherein at least a portion of the covering is sufficiently transparent and wherein the coloring and levels of transparency of the covering, substrate(s) and fluid(s) are selected to allow an observer to the view the progress of the fluid(s) with the unaided eye as the fluid(s) travels along the substrate channels;
wherein the flow of the fluid(s) through the channels is primarily by capillary action.
In one embodiment of an article of the invention the article is designed wherein one fluid and one substrate is present and wherein the covering comprises a top layer and a lower layer, wherein the flow of fluid is viewed through the top layer of the covering and wherein the first major surface of the substrate is closest to the top layer of the covering and the second major surface of the substrate is closest to the lower layer of the covering.
In one embodiment of an article of the invention the article is designed wherein one fluid and one substrate is present and wherein the covering comprises a top layer and a lower layer, wherein the progress of the flow of fluid is viewed through the top layer of the covering and wherein the second major surface of the substrate is closest to the top layer of the covering and the first major surface of the substrate is closest to the lower layer of the covering.
In another embodiment of an article of the invention having a cover, the cover further comprises a scale which is positioned on a portion of the cover through which the progress of the fluid flow may viewed and which extends in the direction of the fluid flow.
In another embodiment of the article of the invention the article further comprises indicia on the cover indicating how to activate the article.
In another embodiment of the article of the invention having a cover the cover comprises two pieces of tape joined together which encase the substrate(s) and the fluid(s), wherein the first piece of tape is transparent single sided adhesive tape and wherein the second piece of tape is a double sided adhesive tape, wherein the single sided adhesive tape is positioned such that the progress of the flow of fluid(s) can be viewed therethrough and wherein the adhesive coated side of the single sided tape is positioned towards the fluid(s) and the substrate(s).
In another aspect the article of the invention comprises:
(a) at least one substrate, each substrate(s) having a microstructured surface, wherein the microstructured surface of each substrate defines a plurality of channels;
(b) at least one solid, wherein the solid(s) are capable upon exposure to heat of forming a fluid;
wherein the article is designed such that it can be manipulated, if needed, at a desired point in time after the solid(s) form fluid(s) upon exposure to heat to allow contact of the fluid(s) with at least some of the channels of at least one of the substrate(s) in order to activate the article; and
wherein the article is designed in such a manner as to provide an indication of the progress of the fluid as it migrates through the channels of the substrate(s).
In one embodiment of the article of the invention the article is designed such that the fluid contacts at least some of the channels of the substrate(s) upon exposure of the solid to heat to form the fluid without any manipulation of the article needed.
In another embodiment of the article of the invention the solid and the fluid formed from the solid upon exposure to heat are separated from the substrate and the fluid contacts the substrate only upon manipulation of the article in order to activate the article.
The present invention also provides an assembly comprising the article of the invention attached to an item selected from the group consisting of food, food additives, biological material, drugs, cosmetics, photographic supplies, drugs, filters, visitor badges, flowers, air fresheners, insect traps, and parking permits.
The substrates useful in the articles of the invention may have various optical properties including but not limited to those selected from the group consisting of retroreflectivity, diffractive properties, diffusive properties, and partial internal reflective properties.
In one embodiment of the present invention the substrate(s) have optical characteristics and the progress of each fluid as it migrates through the channels of a substrate is evidenced by the frustration of the optical characteristics of the substrate.
Various features discussed herein with respect to articles that contain a fluid would also be useful in articles that contain a solid that upon exposure to heat becomes a fluid to the extent that the features are not inconsistent with the requirement that the fluid is formed from the solid.
As mentioned previously it is preferable that the article of the invention have a high level of accuracy. That is, it is preferred that the article records time elapsed as closely as possible to the actual elapsed time. For example, if an article is marked in hour increments and is designed to expire in four hours, it should as closely as possible match the actual elapsed time throughout its course. For some uses rather than others it would be more important to have a highly accurate timer. The level of accuracy can be measured and compared at any unit along the scale including the expiration point and comparing it to the actual elapsed time. Preferably the accuracy value holds true for at least one unit along the scale (which could for example be the expiration point), more preferably for all the units along the scale. The default unit which is used for this test is the expiration point. Preferably the time indicated on the scale is within about xc2x150% of the actual time, even more preferably within about xc2x140% of the actual time, even more preferably within about 30% of the actual time, even more preferably within about xc2x125% of the actual time, even more preferably within about xc2x120% of the actual time, even more preferably within about xc2x115% of the actual time, even more preferably xc2x110% of the actual time, even more preferably within about xc2x15% of the actual time, even more preferably within about xc2x14% of the actual time, even more preferably within about xc2x13% of the actual time, even more preferably within about xc2x12% of the actual time, even more preferably within about xc2x11% of the actual time, even more preferably within about xc2x10.5% of the actual time, and most preferably the same as the actual time.